The introduction of microchannel plate electron multiplier devices to the image tube industry creates serious manufacturing problems. The image tubes require ultra-high vacuum conditions to function properly and the microchannel plate multiplier generates a substantial quantity of gas during tube processing. The microchannel plate electron multiplier selected by the tube industry for efficient electron multiplication properties and compactness in size, consists generally of a porous glass disc. The glass body is treated to render secondary emission properties to the interior of the multitude of glass pores extending through the disc. The larger specific surface area provided by the microscopic pores serve as a haven for absorbed gas molecules which must be removed before an operable image tube device can be produced.
Current methods for processing image tube devices containing the microchannel plate electron multiplier usually consist in inserting the microchannel plate within an open-ended tube body and heli-arc welding one faceplate to one end of the tube. The tube is then transferred to a process station where a photocathode is deposited on another faceplate which is subsequently sealed to the open end of the tube while maintaining the tube assembly in ultra-high vacuum. The problem encountered in tubes processed containing the microchannel plate is reflected in the substantial amount of time required in the evacuation process to assure that the microchannel plate is out-gassed as completely as possible. Substantially long processing times are required since the microchannel plate must remain under evacuation when standard ion pumps are employed to assure that the microchannel plate is thoroughly outgassed. Attempts to decrease the long processing schedules by means of electron bombardment of the microchannel plate have reduced the processing time requirements to a certain extent, however, substantial processing times are still required.
One purpose of this invention therefore is to provide apparatus and methods for substantially decreasing the amount of processing time required for out-gassing image tube devices containing microchannel plate electron multipliers.